Froth flotation separation



March l5, 1960 H. LoGUE 2,928,543

FRo'rH FLoTATIoN SEPARATION Filed Nov. 1o, 1955 2 sheets-sheet 1ATTORNEYS March 15, 1960 L. H. LOGUE 2,928,543

FROTH FLOTATION SEPARATION Filed Nov. l0, 1955 2 Sheets-Sheet 2 IN V ENTOR.

l5 43 42 Leland H. Logue .ATIQRNEYS FROTH FLTATIN SEPARATION Leland H.Logue, Denver, Colo., assignor, by mesne assignments, to DenverEquipment Company, Denver, Colo., a corporation of Colorado ApplicationNovember 10, 1955, Serial No. 546,123

5 Claims. (Cl. 269-169) This invention relates to the froth o'tation artand more particularly relates to improved methods and means forperforming froth flotation separations.

Mechanical type froth flotation apparatus has come into generalacceptance by most flotation operators and many advantages over thepneumatic or air lift machines. There has been a tendency to go tolarger sized equipment in ore milling and this has required theproduction of larger flotation cells. ln almost all pulps, there will bea considerable portion of the solids in liner size ranges and anotherconsiderable portion in substantially coarser sizes.

There is a tendency toward size segregation or stratication in themodern machines with a substantial amount of the finer sizes remainingin the upper portion of the pulp body and another substantial amount ofcoarser sizes remaining in the lowermost portion of the pulp body. Theseconditions do not favor good dotation as the intermediate sizes tend tofloat more readily while the line sizes near the top and the coarsesizes near the bottom cause a density build up that impedes theflotation elli-Y ciency. In addition, an appreciable amount of gangue inline sizes frequently is entrained in the ne concentrate and thusreduces the grade of concentrate.

The coarse sizes in the lower portion of the pulp body are moving underthe intense action of the agitation and exert a scouring action on theliner sizes which reduces the filming effect on such particles andthereby impedes flotation. However, the usual agitation fails to makeprovision for loosening and distribution of the coarse strata forming inthe lower portion of the cell. Even in operations where arrelativelyhigh recovery is obtained at flotation there is a substantial amount ofthe valuable constituent passing from the treatment with the tailingswhich invites recovery if an economical method can be provided.

My invention is based on the discovery that by inducing a high degree ofcirculation along essentially vertical courses within a otation cell, asize segregation of pulp particles can be greatly alleviated if notcompletely eliminated with substantial reduction of tailings losses. Ininducing such circulation I prefer to utilize a free falling movement ofpulp through a downward course of substantial vertical extent whichdevelops a high velocity movement that is highly effective inentrainment of air or other aerating gas and reduces the powerrequirement of the impeller due to the high velocity input of pulp. Ialso utilize a high velocity discharge at the bottom of this verticalcourse which provides a high degree of intermingling of coarser andfiner sizes accompanied by intense gas release and elevating movement ofthe commingled solids.

Accordingly it is an object of this invention to provide a simple,efficient and economical froth flotation process in mechanical typecells which process substantially eliminates size segregation of pulpconstituents in the treatment and thereby improves grade and recovery.

Another object of this invention is to provide a simple,

States Patent C) durable and economical froth flotation cell which mayhave a greatly increased vertical dimension as compared withconventional cells, thereby permitting large volume treatment over asmall floor space and with improved flotation efficiency.

A further object of this invention is to provide a simple, eliicient andeconomical process which permits the circulation of a larger volume ofpulp during a given flotation time and with improved grade and recovery.

Other objects reside in novel details of construction and novelcombinations and arrangements of parts, all of which will be set forthin the course of the following description. Y

One of the advantages of the present invention is that it may beincorporated in machines already installed and in use as well as in newembodiments specially designed for the practice of the invention. it maybe utilized in unit cell operations although it will have its greatesttially the same operation is performed in each cell although the highesteiciency will derive from the utilization of optimum dimensionalrelationship and operating controls.

The practice of the invention will be best understood by reference tothe accompanying drawings in which a preferred embodiment of theapparatus of the present invention has been illustrated. In the drawingsin both views of which like parts bear similar reference numerals:

Fig. l is an end elevation, partially broken to show arrangement ofinterior parts, of a flotation cell utilizing features of the presentinvention and represented as being empty; and t Fig. 2 is a developedsection of a similar cell taken approximately on the line 2 2, Fig. 1and with a fragmentary representation of the arrangement of adjoiningcells in the series of a multiple cell machine and represented as inoperating condition with flows indicated by arrows.

The machine shown in Fig. 2 comprises a three-cell arrangement in whichcell C represents a rst cell of the series, cell C1 an intermediatecell, and cell C2 a last cell of a hog-trough type mechanical machine inwhich a suitable control (not shown) of the tailings discharge from thelast cell as by overliow weir or oat valve control will control the rateof tiow through the machine. Initial feed to the machine usually isthrough a feed box and submerged inlet (not shown). Since these featuresare old and well known in the art, detailed description and illustrationappears unnecessary.

Each of the cells C, C1, and C2 will comprise a front wall 12, a rearwall 13, two side walls 1d and a bottom 15. Preferably the front wall 12inclines forwardly in its upper portion to provide an enlargedspitzkasten effect while rear wall 13 inclines inwardly as shown tocrowd the froth bed toward overow lip 16 at the top of wall 12. Thisarrangement provides a large area near the surface of the pulp bodywhich is out of the path of the circulating llow as will be subsequentlydescribed and assists in the collection and discharge of the frothconcentrate.

Cell C1 has one or a plurality of pulp inlets 18, shown in Fig. 2 asthree in number, and these inlets function as the tailings discharge ofthe preceding cell in the series which is the cell C of Fig. 2. Thecombination of feed upper surface and a plurality of sweeping vanes 28on its` under surface.

An impeller Z6V is mounted on the' A hollow column 3d issupported in adepending posi-v Y tion from the lower endiof bearing assembly 22`in`encompassing relation toshaft 21. The column 30 extendsthroughoutsubstantially the vertical extent of cell C1 and carries alaterally extending cover member 31 at its lower .end whichoverhangsimpeller with its under surface y providing only a slight clearance withthe tops of bladesV 27 onthe impeller. Y Y Y Y A plurality of pulpintake openings 33 Vare located in the upper portion of column near butbelow liquid level 19 and air intake openings 34 are located infV theVcolumn above the liquid level. yIf Vtheaeration, isV to.V utilizeatmospheric air the openingsr34V will be left un`.

plugged, but if an aerating gas under lpressure is used,.a ll but one ofsaid openings will be plugged and the remain'- ing one connected as bythreaded nipple with a header or, For best r`e" sults the liquid headover openings 33 should correspondV other source of gas supply (notshown).

to the showing in Fig.V l, and if a given operation produces a greaterfroth depth or lowering of liquid level 19, onek or more slots 40 shouldbe inserted in guide member` 414 to provide a weir overflow above lip 16and .thereby bring the liquid level into proper relationship withopenings 33.

fraot the flow of aerating gas downwardly through said b e. t

Due to the substantial distance between the openings 33 and the impeller26 andthe unrestricted fall of the pulp onto the impeller, such pulpattains a relatively high velocity movement before reaching the impellerwhich induces a high degree of gas entrainment in the cascading action.The impeller is rotated at a speed which will discharge the pulp-gasintermixture at a rate at least equal p to therate of its delivery tothe impeller, and in preferred practice,l at an even higherrate. As aconsequence pulp enters column 30 in a volume permitted `by the area ofopenings 33 collectively under the hydrostaticV head of the liquidextending to level 19`. The shield 36'prevents a vortex formation whichmight recirculate froth eoncen- Y trate and the circulatory actioneffectively retards size stratification of pulp particles.

Whenever'feed entering a given cell tends to cause such stratification'by delivering too `large a proportion of coarse sizes into the lowerpartof the pulp body, the` impeller Ydischarge eifec'tsa displacementaction in which v a substantially. higher percentage `of ner sizesreplaces the coarser sizes elevated by the Vupward sweep of pulp ithrough the cell. In the usual flotation cell, this elevat- Anannularfbatfle 35 divides the Yupper hollow portion ofcolumn 3i) into aninner air passage andan outer pulp passage. Thisbaflie may-be of anysuitablelength but should extend below the pulp intakeopenngs?, so thatthe entering pulp streams are diverted withoutconverging and thus fallby gravity in an unimpeded descent tothe impeller. ln order to avoid anyvortex'formation at the surface which might remove aV substantialquantity ofthe froth concentrate; l provide' an annular shield 36 aboveopenings 33. Other shapes of shield may be provided but the annularformi is simple to construct andY is easily connected. e v v As shown inFigs. 1 and 2, the cell bottom A1S maybe providedvwith a centralraperture 42 normally closed by a plug 43 and this opening Vwill be usedfor draining the machine as required, or if desired, a suitable Vgasline may be connected for the supply of additional aerating gas, or

reagent. The machine illustrated has the bearing mem`l ber 22 detachablymounted on superstructure 20 so that the impeller 26 and column 30 maybe installed and removed as a unit. In addition, an access opening 45closed by a plug 46 permits separate mounting'and removal of theimpeller. Also as shown, the spacing be-v tween the impeller may bevaried by adjustment of bolts 48 inslots 49.

The practice of the invention in a machine such as illustrated in Fig 2will be described. Aconditioned pulp is fed continuously toa first cell,such'as cell C, flows'` through the openings 18 to iillrthe next cellCl-which may l ybe any number of intermediate cells, and `again passesv`through openings 13 to till a last cell Cz'gwhichghas, a .e

continuous, regulated discharge suchl as anfadjustable weir (not shown).The flow permitted by the` openings 18 provides a substantially uniformliquid level 19in all cells. The pulp will contain one portion of solidsin a coarser size range and another portion of ner sizes, the

actual size distribution varying withfeach ore treated.

Each of said cells will have a circulation of the'type l `depicted inFig. 2 in which the impeller 26 will befrotated at a peripheral speedonvt'ne order of 1600 feet per minute and all feed thereto entersthrough theV plurality formation occurs in the vascending pulp, column.

ing movement is Voffset byfresulting downward currents as the upperportion of the cell has no capacity `to relieve itself from the ,inputof pulp. However in the present arrangement, the input and dischargecapacity of the upper portion of the solids arefree to descend onlywithin the enclosure of thelcolumn.` v

A s a`result,.a high degree of mixing Yof tine and coarse sizesaccompanied `by intense gas release in tine bubble In a typical testinstallation: in ajcell of approximately 375 gallons capacityA andarranged substantially as shown in Figi2, it was determined that thepulp was recirculating at a'rate ofbetween'450 and 500 gallonsperminute. Average flotation time in such` installations is on the order oftwo minutesso the entire pulp volume recirculates ,between'two and`three times'within the dotation time period providedfor such cell. v

The flotation operation. just described has the effect of increasingVplmtfcapat`y as a higher volume of pulp can be treatedecientlyin ashorter time than in conventional operations. A greatly improved gradeand recovery is attained. impeller speeds are reduced with consequent`power savings and reduced wear. Y This was demonstrated in'acomparative test in a commercial milling operation; Threestandard cellswere subjected to comparative tests Yforten day periods with sizeanalysis of concentrateproducedV in each cell. The ten day averageestablished that cell No. 1 had 33 percent in the plus l0() size range,cell No. 2, 31 percent plus 100 and cell No. 3, 33' percent plus' `100.Y, f e Y Theimiddl'e No. 2 cell was then modiliedto correspond with thearrangement shown in Fig. 2, cells Y1 and 3 were wasrundertalcen. Theaverage analysis was as follows:

of openings 33 in column 30 from near but below theI l liquid level 19.This entering pulp is directed by the Aanff nular baille 35 into.gravitational fallinitially separated,`

cell No.1, 27 percent plus 100,V cell No. 2, 45 percent plus 100, andcell No. 3, '34 percentplus'lOO. The foregoing-,test results.` arercitedkas typical, of the degree of concentration of thevcoarsersiz'es Ywhichcan be attained in the practice of thepresent invention.

*The'maehineillustrated in the drawings is a Denver Equipment Companyho`g-troug hY type modified to em-Y body features `of the presentinvention. While such a Vmachine is well suited to thepracticeof myinvention, it

. will be understood that other standard mechanical-type` cells may besimilarly modifiedV for the practice of the invention. `Howeveigthe`invention lends itself to em-` bodiment in specially designed cells'ofmuch greater depth than'conventional cells.' Theextension of depthapparf` Aently does not lessenmetallurgical ,efficiency and in someVinstances may'imp'rvef it, and the resulting increase in` cell. is`substantially balanced and` f Y s cell capacity permits substantialincrease in plant capacity without enlargement of plant area and noincrease in operator requirements. Y

Changes and modifications may be availed of Within the spirit and scopeof the invention as defined in the hereunto appended claims.

I claim:

l. In the froth flotation art in which a conditioned pulp is subjectedto a succession of flotation treatments at progressive stages of acourse of flow with arpredetermined otation time at each stage, theimprovement which comprises maintaining a body of pulp of substantialvertical extent subject to continuous feed and discharge at each stage,inducing a circulatory ow within said body so as to direct an elevatingcomponent of movement to substantially all the solids in the lowerportion of said body and an unimpeded gravitational fall to asubstantial portion yof the solids in the upper portion of said body andbelow the surface thereof, supplying an aerating gas for entrainment inthe pulp in said gravitational fall, and controlling the volume andvelocity of pulp in said gravitational fall so as to recirculate a majorpart of the pulp volume during said flotation time.

2. In the froth flotation art in which aconditioned pulp is subjected toa succession of flotation treatments at progressive stages of a courseof flow with a predetermined ilotation time at each stage, theimprovement which comprises maintaining a body of pulp of substantialvertical extent subject to continuous feed and discharge at each stage,inducing a circulatory flow within said body so as to direct anelevating component of movement to substantially all the solids in thelower portion of said body and an unimpeded gravitational fall to asubstantial portion of the solids in the upper portion of said body andbelow the surface thereof, supplying an aerating gas for entrainment inthe pulp in said gravitational fall, controlling the volume and velocityof pulp in said gravitational fall so as to recirculate a major part ofthe pulp volume during said flotation time, and removing a concentrateby `overflow at a distance from said circulatory ow.

3. A processas dened in claim 1 in which the circulatory flow isdirected to cause a continuous intermingling of liner and coarser sizesin the pulp.

4. In the froth liotation art in which a conditioned pulp is subjectedto a succession of flotation treatments at progressive stages of acourse of ow with a predetermined otation time at each stage, Vtheimprovement which comprises maintaining a body of pulp of substantialvertical extent subject to continuous feed and discharge at each stage,inducing a circulatory flow within said body so as to direct anelevating component of movement to substantially all the solids in thelower portion of said body and an unimpeded gravitational fall to asubstantial portion of the solids in the upper portion of said body andbelow the surface thereof, supplying an aerating gas for entrainment inthe pulp in said lgravitational fall, and controlling the volume andvelocity of pulp in said gravitational fall so as to recirculate aquantity of pulp in excess of the pulp volume of said stage during saidotation time.

V5. In the froth otation art in which a conditioned pulpV is subjectedto a succession of otation treatments at progressive stages of a courseof flow with a predetermined flotation time at each stage, theimprovement which comprises maintaining a body of pulp of substantialvertical extent subject to continuous feed and discharge at each stage,inducing a circulatory flow within said body so as to direct anelevating component of movement to substantially all the solids in thelower portion of said body and an unimpeded gravitational fall to asubstantial portion of the solids in the upper portion of said body andbelow the surface thereof, supplying an aerating gas for entrainment inthe pulp in said gravitational fall, and controlling thevolume andvelocity of pulp in said gravitational fall so as to recirculate thepulp volume of said stage a plurality of times during said otation time.

References Cited in the le of this patent UNITED STATES PATENTS1,556,083 Daman oct. 6, 192s 1,921,220 Daman Aug. 8, 1933 2,612,358Daman -sepr. so, 1952

